College Park, Maryland      June 6 - 10 , 2004

MP40: Structural Phase Transitions in Cd2Re2O7

J. He (University of Tennessee, Knoxville; Oak Ridge National Laboratory), B. Chakoumakos (Oak Ridge National Laboratory), D. Mandrus (University of Tennessee, Knoxville), M. Guttmann, C. Wilson (CLRC Rutherford Appleton Laboratory, UK), J. Gardner (National Research Council, Chalk River, Ontario, Canada)

The structural phase transitions at and below T* ~ 200 K in the pyrochlore oxide, Cd2Re2O7, have been the subject of a number of studies, however, the exact nature of these structural distortions and symmetry changes has not been completely elucidated. Accompanying with the subtle structural changes are dramatic changes in the resistivity and magnetic susceptibility, and superconductivity is observed at Tc = 1.0 K. On the other hand, the continuous cubic-to-tetragonal structural transition at T*, the breaking of inversion symmetry and the sustained metallic behavior on both sides of T* suggest this compound as the first example of “metallic ferroelectricity” proposed by P.W. Anderson in 1960s. We have collected single-crystal neutron diffraction data at the SXD instrument at ISIS, and powder diffraction data at C-2,NPMR, Chalk River Laboratory, using isotopically enriched crystalline specimens. Data sets for several temperatures have been collected. We are testing a variety of lower symmetry structural models to determine the best description of the intermediate- and low-temperature range structural modifications before the onset of superconductivity.

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